The present invention relates to the field of communications, and, in particular, a network communications system wherein synchronized voice services are provided to a remote synchronous network over a non-synchronous shared medium LAN integrated with a gateway coupled to the remote synchronous network.
As computers become more and more cost effective for the everyday consumer and for small businesses, such computers become more plentiful for use within local area environments such as homes, office buildings and the like. For example, within a home a person with a computer in the bedroom, and another in the living room, may want to share common files, utilize a common digital subscriber line (DSL), or otherwise transfer information between the computers. Accordingly, various technologies are being developed for computer interconnection of multiple computers located within such environments. One example of such technologies is the Home Phoneline Network Alliance (HPNA) technology for Local Area Network (LAN) computer interconnection which utilizes existing telephone lines within the local environment for the transmission of data packets between the computers. The HPNA technology is implemented in the Broadcom Corporation Model Number BCM 4210 Controller product and is set forth in U.S. patent application Ser. No. 60/196,002 entitled xe2x80x9cHome Phone Line Network and Apparatusxe2x80x9d, the content of which is incorporated by reference herein.
FIG. 1 shows in block diagram form a general home networking environment within which the present invention can be implemented. Home network 10 includes existing (installed) plain old telephone service (POTS) wiring 12, network clients 14, the computer port side of modem 16 and fax 18. POTS wiring 12 provides wiring infrastructure used to network multiple clients at a customer premises (e.g., home) 20. POTS wiring 12 can be conventional unshielded twisted pair (UTP) wiring that is generally routed internally in the walls of the customer premises 20 to various locations (e.g., rooms) within the customer premises. Subscriber loop 22 (also called a xe2x80x9clocal loopxe2x80x9d) is a physical wiring link that directly connects an individual customer premises 20 to the Central Office through telephone interface 24, a demarcation point between the inside and outside of customer premises 20. Of particular importance for residential networks are systems that provide communication between computers as reliably and with as high a data rate as possible. Communication over residential telephone wiring is provided through inventive frame-oriented link, media access and physical layer protocols and implementation techniques associated therewith.
Given the HPNA environment, an opportunity exists integration of the HPNA environment with voice services for transfer of voice message (from a caller) to a voice services recipient(a called party) over, for example, a cable modem system, or a Wide Area Network (WAN), or a Global Network such as the Public Switched Telephone Network (PSTN) or Internet Protocol (IP) Network. FIG. 2 depicts such an integrated environment. As can be seen in FIG. 2, a connection point in the home to the telephony world (e.g., the world of video, voice, high speed data network traffic), could be provided to a home user through cable modem 30 which would include an HPNA transceiver. The cable modem system provider may also wish to accommodate providing telephone service along with high speed data service. A home computer user, rather than using a traditional modem to connect to an internet service provider, would find it convenient to utilize cable modem 30, taking advantage of the very high speed data service provided by the cable modem. Having a cable modem customer, the cable modem provider may also find it commercially beneficial to offer video feeds, and telephone service over the same cable modem network. Cable modem 30 would be coupled to Headend 32 over Hybrid Fiber Coaxial (HFC) network 34. Headend 32 would include internet router 36 having Cable Modem Termination System (CMTS) 38 for communication with the Internet. A CM/CMTS system can be implemented using the Broadcom Corporation Model Number BCM3210Cable Modem Termination System product and is described in detail in U.S. patent application Ser. No. 09/501,850 entitled xe2x80x9cCable Modem System with Sample and Packet Synchronizationxe2x80x9d, which is incorporated by reference herein.
Referring now to FIG. 3, there is shown a more simplified example of a voice services communications network, along with a depiction of the synchronous and asynchronous aspects associated with particular portions of the network. Telephone handset 40 is connected to terminal 42 which consists in part of: (a) voice codec 44, which converts between analog signals and. sampled digital signals at a sample rate which is determined by a clock in the codec (hereinafter xe2x80x9cClock 2xe2x80x9d), and (b) HPNA network interface(I/F) 46a, which assembles the voice samples into a packet (e.g., such as a layer-2 frame type) which is then transmitted on HPNA network 48 to gateway 50. Gateway 50 receives the HPNA packet at counterpart HPNA network I/F 46b and queues it for transmission by Wide Area Network (WAN) interface 52. This transmission is made synchronous to a gateway clock (hereinafter xe2x80x9cClock 1xe2x80x9d) in gateway 50 which is determined by the access equipment at the other end of the DOCSIS link 56, e.g., the CMTS, should gateway 50 be part of cable modem 30 as seen in FIG. 2. Clock 1 is made synchronous in gateway 50 in accordance with the teachings of U.S. patent application Ser. No. 09/501,850 referenced above. The packet sent up WAN DOCSIS link 56 is routed across global Internet Protocol (IP) network 54 to the destination, e.g., a comparable gateway/terminal combination (or equivalent) to that of gateway 50 combined with terminal 42. Similarly, voice packets received over the DOCSIS WAN link 56 by WAN I/F 52, are transmitted by gateway HPNA I/F 46b over HPNA network 48 to terminal HPNA I/F 46a, where the packet is disassembled back into samples which are converted by voice codec 44 back into analog signals for telephone handset 40. Included in FIG. 3 is a depiction of information transition 60 from the DOCSIS domain (synchronous to Clock 1) to the asynchronous HPNA network (which introduces some jitter), and transition 62 from the asynchronous HPNA network to the terminal voice codec domain (synchronous to Clock 2).
A need therefore exists for a effective transport of synchronized voice services over a non-synchronous network. The present invention provides a solution to such need.
In accordance with the present invention a method is providing for synchronizing one or more synchronous terminals with one or more synchronous endpoints, each synchronous terminal and each synchronous endpoint having an asynchronous communications network coupled between at least one synchronous terminal and at least one synchronous endpoint. A synchronization protocol (SP) is established between a synchronous terminal and a synchronous end point by providing a gateway between the asynchronous communications network and the synchronous end point, the gateway communicating with the synchronous terminal over the asynchronous communications network in accordance with the synchronization protocol. The synchronization protocol includes sending a message (referred to herein as an xe2x80x9cSP packetxe2x80x9d) from the gateway to the synchronous terminal, the SP packet containing a timestamp identifying a clock associated with the synchronous end point. The synchronous terminal establishes a clock associated with the synchronous terminal by creating a clock estimate based upon the timestamp message and measurements of the access jitter introduced by the asynchronous communications network such that the clock associated with the synchronous terminal enables packet sampling and transmission onto the asynchronous communications network to and from the synchronous terminal to be synchronized with the clock associated with the synchronous end point.